Why the `libstdc++.so` compiled from source seems to be incorrect?

I try to compile gcc and libstdc++(as a part of gcc) from the source code.

With:

$ git clone https://github.com/gcc-mirror/gcc.git # mirror repo$ cd gcc && md build && cd build$ ../configure --enable-languages=c,c++,lto     \    --enable-lto --prefix=/usr/local            \    --enable-shared --enable-host-shared        \    --with-gnu-as --with-gnu-ld                 \    --enable-threads=posix                      \    --enable-__cxa_atexit                       \    --enable-gnu-indirect-function              \    --disable-werror --enable-checking=release  \    --disable-multilib --enable-linker-build-id \     --with-linker-hash-style=gnu                \    --disable-bootstrap --disable-libssp        \    --enable-default-ssp$ make all -j4 && make install

However, when I try to link libQt6Core.so into my project with the above compiler and libstdc++, ld complains like:

/usr/bin/ld: /lib/../lib64/libQt6Core.so: undefined reference to `operator new(unsigned long)@GLIBCXX_3.4'

Also, I find:

$ strings /usr/local/lib64 | grep GLIBCXX # get libcxx api version

only gives:

GLIBCXX_FORCE_NEWGLIBCXX_DEBUG_MESSAGE_LENGTH

But with system libstdc++ I can see string like GLIBCXX_3.4.20 and so on.

So why my libstdc++ lib seems get something wrong?